MANILA (AFP) - Underdog Manny Pacquiao said on Wednesday he has a simple tactic to beat American favourite Floyd Mayweather in history's richest fight by two longtime rivals for the planet's top pound-for-pound boxer crown.

"Use my left and right (fists)," the Filipino boxing hero told reporters when asked how he planned to deal with his undefeated foe's height and reach advantage, as well as famed defensive skills.

"If I hurt him, I expect him to run. Otherwise, he might fight me toe-to-toe."

The Philippines is in the throes of Pacmania as the 36-year-old, dubbed The National Fist by local media, is set to fly to the United States to train for the May 2 Las Vegas bout.

The 38-year-old Mayweather, tipped as the favourite by bookmakers after announcing the megabucks fight last weekend, has not lost any of his 47 fights, in which he has scored 26 knockouts.